The present invention relates to a rotation sensor attached to a shaft or other object for assembly experiencing an offset of the angle of relative rotation at different positions in the axial direction and detecting by a non-contact method the difference in angle of relative rotation of the object for assembly and a measurement circuit using the rotation sensor and relates to a rotation sensor for detecting by a non-contact method the angle of rotation (position) of the object for assembly in addition to the angle of relative rotation.
To detect the rotational torque acting on the steering wheel shaft of an automobile comprising a drive shaft and a driven shaft coupled via a torsion joint, sometimes a rotation sensor is used as a relative rotation angle detector for detecting the angle of relative rotation of the steering wheel shaft.
As an example of such a rotation sensor, Japanese Examined Patent Publication (Kokoku) No. 63-45528 discloses a configuration forming notches at predetermined positions in the longitudinal direction of two conductive members comprised of cylindrical shapes, rotating a shaft attached with a conductive member relatively so as to change the area of the conductive member cutting across the magnetic field and generate an eddy current in the conductive member and thereby change the inductance of a coil, and detecting the amount of offset of the angle of relative rotation at the shaft by a non-contact method.
According to this configuration, since the area of the conductive member cutting across the magnetic field is changed by the change in relative position of two conductive members, in order to accurately detect the amount of offset of the angle of rotation of the shaft, it is necessary to make the amount of offset of the angle of the rotation of the two shafts and the magnitude of the eddy current occurring in the conductive members proportional. Structurally, the area of a conductive member cutting across the magnetic field is proportional to the amount of offset, but what is necessary is to make the intensity of the magnetic field cut across by the two conductive members constant.
The magnetic field generated from the coil is however distributed substantially uniformly in the circumferential direction, while the distribution of the magnetic field on the rotation axis direction or radial direction of the coil is not uniform. Therefore, to ensure sensing with good linear characteristics, the two conductive members have to be assembled to overlap without a clearance. To improve the detection precision of the angle of rotation of the shaft, there is the problem that assembly precision continues to be strictly required.
Further, in a conventional measurement circuit of a rotation sensor, an AC current flows to an excitation coil provided at a stationary core and electrically connected to an oscillation circuit. The impedance of the coil changes depending on the angle of relative rotation of the first and second rotors. Further, the oscillation frequency of the oscillation circuit fluctuates in accordance with the change in the impedance of the excitation coil. Therefore, in this measurement circuit, the practice has been to count the pulse signals generated from the oscillation circuit by a pulse counter so as to detect the oscillation frequency and to measure the angle of relative rotation of the first rotor and the second rotor.
In this measurement circuit, however, the oscillation frequency of the oscillation circuit fluctuates in the range of 98 kHz to 108 kHz with respect to a change in the impedance of the coil. The circuit normally measured the number of pulses by a resolution for counting the pulse signals in a time of 5 ms. Therefore, if this measurement circuit is used to detect the torque acting on for example the steering wheel shaft of a vehicle, there was the problem that time was taken for counting the pulses by a pulse counter and the response became poor. For example, when the oscillation frequency of the oscillation circuit fluctuates from 100 kHz to 105 kHz due to this resolution, the number of pulses becomes measured by a fluctuation from 500 pulses to 525 pulses, that is, by an amount of fluctuation of 25 pulses.
Further, in this measurement circuit, if the time for counting pulses of the pulse counter is shortened to improve the response, the amount of fluctuation of the number of pulses becomes smaller and the resolution falls, so there is the problem that detection of fluctuation of the oscillation frequency becomes difficult.
On the other hand, the rotation sensor shown in FIG. 53 is comprised of a stationary magnetic member 1 having a coil and a magnetic material rotor 2 having irregularities on its outer circumference between which is arranged, in a predetermined gap, a metal rotor 3 having a plurality of metal teeth 3a. This rotation sensor has the plurality of metal teeth 3a arranged at equal intervals in the circumferential direction and generates an eddy current in the metal teeth 3a when the metal teeth 3a cut across the AC magnetic field with the irregular distribution due to the relative rotation of the two rotors 2 and 3. This eddy current fluctuates due to the angle of relative rotation between the two rotors 2 and 3. Therefore, the rotation sensor detects the angle of relative rotation of the two rotors 2 and 3, that is, the angle of relative rotation between two relatively rotating members, by measuring the change in the impedance of the coil caused due to the fluctuation in the eddy current induced inside the members.
A rotation sensor using such an irregular distribution AC magnetic field, however, is governed in characteristics by two parameters, that is, the fluctuation xcex94B of the magnetic flux density and the boundary area xcex94xcex8 of the intensity of the magnetic field in the distribution produced as shown in FIG. 54 showing the fluctuation in magnetic flux density in the circumferential direction in the gap. That is, the rotation sensor has a higher sensitivity of detection of the angle of rotation the larger than fluctuation xcex94B of the magnetic flux density and has a good linearity of detection output the smaller the boundary area xcex94xcex8 of the distribution of the magnetic field.
The rotation sensor, however, suffers from the following problem if making the degree of irregular distribution of the AC magnetic field due to the size of the gap larger.
As is well known, in a magnetic circuit, fluctuations of the effective specific magnetic permeability due to the size of the gap deviate from a linear characteristic. That is, in a magnetic circuit, the smaller the gap, the larger the fluctuation of the effective specific magnetic permeability. Since the metal rotor 3 is arranged in the gap in this way, if considering the manufacturing precision and rotational precision of the rotor, normally in the rotation sensor, the gap G1 is desirably set to at least 1 mm as shown in FIG. 53. An amount of change of the gap of several millimeters is required in order for the rotation sensor to obtain a suitable detection sensitivity. That is, the rotation sensor has to be of a size giving an amount xcex94G of change of the gap (=G2xe2x88x92G1) accompanying irregularity of the magnetic material rotor 2 of several millimeters.
On the other hand, in the rotation sensor shown in FIG. 53, the thickness of the magnetic material rotor 2 is changed cyclically corresponding to the plurality of metal teeth 3a along the circumferential direction. Therefore, since the gap formed in the circumferential direction between the fixed magnetic member 1 and magnetic material rotor 2 is step-like in shape, when magnetic flux flows from the core material with the high magnetic permeability into the air with the low magnetic permeability, it characteristically concentrates at the corner portions of the core material. Therefore, due to the magnetic flux concentrating at the corner portions, in this rotation sensor, there was the problem that the boundary area xcex94xcex8 of the distribution of the magnetic field became large and had a detrimental effect on the linearity of the detection output.
Further, the rotation sensor, for example, the rotation sensor disclosed in Japanese Unexamined Patent Publication (Kokai) No. 7-139905, could measure a rotational angle of within 180 degrees in the left and right directions (within one turn), but could not measure an angle of rotation exceeding 180 degrees. Further, it was not possible to measure which of the right or left positions the measured angle of rotation was and it was necessary to measure the rotational position separately.
In this case, depending on the application, the rotation sensor is sometimes required to measure the rotational torque rather than the angle of rotation.
The present invention was made in consideration of the above point. A first object of the present invention is to provide a rotation sensor superior in detection precision relating to the angle of relative rotation of an object for assembly.
Further, a second object of the present invention is to provide a rotation sensor able to measure the angle of rotation (position) at a high precision in addition to the angle of relative rotation of the object for assembly.
Further, a third object of the present invention is to provide a measurement circuit of a rotation sensor having a high resolution with respect to measurement of the angle of relative rotation of the object for assembly and able to improve the response.
A fourth object of the present invention is to provide a rotation sensor enabling easy assembly without requiring precision of assembly to the object for assembly and superior in detection precision relating to the angle of relative rotation.
A fifth object of the present invention is to provide a rotation sensor small in size, having a linear detection output, and high in sensitivity of detection.
A sixth object of the present invention is to provide a rotation sensor able to differentiate whether a rotation position is left or right, able to measure even an angle of rotation of over 180 degrees, and able to measure the angle of rotation and/or rotational torque.
To achieve the first and fourth objects, a rotation sensor of a first aspect of the present invention is provided with a first rotor fixed at a predetermined position in an axial direction of a shaft, a second rotor fixed to said shaft adjoining said first rotor, and a magnetic core arranged around said first rotor and having a resonance coil forming a magnetic circuit together with said first rotor, wherein said first rotor is formed by a magnetic material comprised of an insulator, an irregular magnetic field is formed with said magnetic core, and said second rotor is provided with a conductor cutting across areas of different intensities of the irregular magnetic field in accordance with a difference in angle of rotation when a difference in angle of relative rotation arises between the shaft position where the first rotor is fixed and the shaft position where the second rotor is fixed.
To achieve the first and fifth objects, a second aspect of the present invention provides a rotation sensor provided with a first rotor formed from an insulating magnetic material and attached to a predetermined position in an axial direction of a rotating first shaft, a stationary core fixed to a fixing member and having a core body and an excitation coil carrying an AC current and forming a magnetic circuit working with said insulating magnetic member, and a second rotor attached to a second shaft rotating relative to said first shaft adjoining said first rotor and arranged between said first rotor and said stationary core and detecting an angle of relative rotation of said first and second shafts, said first rotor being provided with conductor layers at predetermined intervals along a circumferential direction and the second rotor being formed with conductor teeth at intervals corresponding to said conductor layers.
Preferably, said insulating magnetic material and said core body are formed by an insulating material comprised of a mixture of a thermoplastic resin and a soft magnetic material and the content of the soft magnetic material is at least 10 vol % to not more than 70 vol %.
To achieve the first and third objects, a measurement circuit of a rotation sensor of a third aspect of the present invention provides a rotation sensor provided with a first rotor formed from an insulating magnetic material, a stationary core having a core body and an excitation coil carrying an AC current and forming a magnetic circuit working with said insulating magnetic material, and a second rotor arranged between said first rotor and said stationary core and measuring an angle of relative rotation of said first and second rotors, further provided with an oscillating means for generating an oscillation signal of a specific frequency, a phase shifting means for shifting a phase of said oscillation signal in accordance with a magnitude of an eddy current generated at said second rotor, a shift detecting means for detecting an amount of phase shift of said shifted oscillation signal, and a measuring means for measuring an angle of relative rotation based on said detected amount of phase shift.
That is, the sensor detects the phase shift of the oscillation pulse signal applied to the excitation coil forming the magnetic circuit in accordance with the magnitude of the eddy current arising in the second rotor and measures the angle of relative rotation of the first rotor and the second rotor from the relationship of the detected amount of phase shift and the angle of relative rotation.
To achieve the second and sixth objects, a fourth aspect of the present invention provides a rotation sensor provided with a first rotor having a plurality of first conductor layers arranged at predetermined intervals along a circumferential direction, a second rotor having an insulating magnetic layer and a second conductor layer, rotating together with said first rotor, and rotating relative to said first rotor within a predetermined angle, a fixing member having an excitation coil and a core formed from an insulating magnetic material and holding said excitation coil, and an oscillating means connected to said excitation coil and generating an oscillation signal of a specific frequency, further provided with a displacement sensor having a movable magnetic core moving in a rotation axis direction of said rotor along with rotation of said second rotor and a coil connected with said oscillating means and working with said moving magnetic core, and detecting a change of coil inductance based on movement in the rotation axis direction of said movable magnetic core.
Preferably, the sensor is provided with, as said excitation coil, at least one of a relative rotation angle coil for detecting an angle of relative rotation accompanying relative rotation of said first and second rotors and a rotation angle coil for detecting an angle of rotation of said first and second rotor with respect to said fixing member.
More preferably, the sensor is further provided with a first signal processing means for processing an output signal from said relative rotation angle coil, a second signal processing means for processing an output signal from a means for measuring said relative angle of rotation or an output signal from said rotation angle coil and a displacement sensor, and a means for measuring the angle of rotation.
Further, to achieve the second and sixth objects, a fourth aspect of the present invention provides a rotation sensor provided with a first rotor having a plurality of first conductor layers arranged at predetermined intervals along a circumferential direction, a second rotor having an insulating magnetic layer and a second conductor layer, rotating together with said first rotor, and rotating relative to said first rotor within a predetermined angle, a fixing member having a relative rotation angle coil for detecting an angle of relative rotation accompanying relative rotation of said first and second rotors, a rotation angle coil for detecting an angle of rotation of said first and second rotor, and a core formed from an insulating magnetic material and holding said relative rotation angle coil and rotation angle coil, and an oscillating means connected to said relative rotation angle coil and rotation angle coil and generating an oscillation signal of a specific frequency, further provided with a displacement sensor having a movable magnetic core moving in a rotation axis direction of said second rotor along with rotation of said second rotor and a coil connected with said oscillating means and working with said moving magnetic core, and detecting a change of coil inductance based on movement in the rotation axis direction of said movable magnetic core.
Preferably, the sensor is further provided with a first signal processing means for processing an output signal from said relative rotation angle coil, a second signal processing means for processing an output signal from a means for measuring said relative angle of rotation and an output signal from said rotation angle coil and a displacement sensor, and a means for measuring the angle of rotation.
More preferably, the sensor is further provided with a pitch sensor having a conductor piece and insulating layer and a coil connected to said oscillating means and working with said conductor piece, one being provided at said fixing member and the other at said second rotor, and detecting a change of coil inductance based on rotation of said second rotor.
More preferably, the second signal processing means processes a signal so as to output the same signal as an output signal at an upper limit point and a lower limit point of an output signal from said rotation angle coil near the upper limit point and lower limit point.
Further, to achieve the second and sixth objects, another aspect of the invention according to the fourth aspect provides a rotation sensor provided with a first rotor having a plurality of first conductor layers arranged at predetermined intervals along a circumferential direction, a second rotor having an insulating magnetic layer and a second conductor layer, rotating together with said first rotor, and rotating relative to said first rotor within a predetermined angle, a fixing member having an excitation coil and a core formed from an insulating magnetic material and holding said excitation coil, and an oscillating means connected to said excitation coil and generating an oscillation signal of a specific frequency, further provided with a displacement sensor having a first gear member fixed to said fixing member, a second gear member having first and second gear parts with different number of teeth, said first gear part engaging with a third gear part formed at said second rotor and the first gear member, a slider having a fourth gear part engaging with said second gear part and a third conductor layer, being transmitted the rotation of said second rotor reduced in speed, and comprised of a magnetic material moving in a rotational direction of said second rotor, and a coil member having a coil provided at said fixing member and connected to said oscillating means and detecting a change of coil inductance between said third conductor layer and coil based on rotation of said first and second rotors.
Preferably, the sensor is provided with, as said excitation coil, at least one of a relative rotation angle coil for detecting an angle of relative rotation accompanying relative rotation of said first and second rotors and a rotation angle coil for detecting an angle of rotation of said first and second rotor with respect to said fixing member.
More preferably, the sensor is further provided with a first signal processing means for processing an output signal from said relative rotation angle coil, a second signal processing means for processing an output signal from a means for measuring said relative angle of rotation or an output signal from said rotation angle coil and a displacement sensor, and a means for measuring the angle of rotation.
Further, to achieve the second and sixth objects, another aspect of the fourth aspect of the present invention provides a rotation sensor provided with a first rotor having a plurality of first conductor layers arranged at predetermined intervals along a circumferential direction, a second rotor having an insulating magnetic layer and a second conductor layer, rotating together with said first rotor, and rotating relative to said first rotor within a predetermined angle, a fixing member having a relative rotation angle coil for detecting an angle of relative rotation accompanying relative rotation of said first and second rotors, a rotation angle coil for detecting an angle of rotation of said first and second rotor, and a core formed from an insulating magnetic material and holding said relative rotation angle coil and rotation angle coil, and an oscillating means connected to said relative rotation angle coil and rotation angle coil and generating an oscillation signal of a specific frequency, further provided with a displacement sensor having a first gear member fixed to said fixing member, a second gear member having first and second gear parts with different number of teeth, said first gear part engaging with a third gear part formed at said second rotor and the first gear member, a slider having a fourth gear part engaging with said second gear part and a third conductor layer, being transmitted the rotation of said second rotor reduced in speed, and comprised of a magnetic material moving in a rotational direction of said second rotor, and a coil provided at said fixing member and connected to said oscillating means and detecting a change of coil inductance between said third conductor layer and coil based on rotation of said first and second rotors.
Preferably, the sensor is further provided with a first signal processing means for processing an output signal from said relative rotation angle coil, a second signal processing means for processing an output signal from a means for measuring said relative angle of rotation and an output signed from said rotation angle coil and a displacement sensor, and a means for measuring the angle of rotation.
More preferably, the sensor is further provided with a pitch sensor having a conductor piece and a coil connected to said oscillating means and working with said conductor piece, one being provided at said fixing member and the other at said second rotor, and detecting a change of coil inductance based on rotation of said second rotor.
More preferably, the second signal processing means processes a signal so as to output the same signal as an output signal at an upper limit point and a lower limit point of an output signal from said rotation angle coil near the upper limit point and lower limit point.